372 research outputs found
Pressure, Resistance, and Current Activation of Anisotropic Compressible Hall States
Thermodynamic and electric properties of anisotropic compressible Hall states
at higher Landau levels are studied using a mean field theory on the von
Neumann lattice basis. It is shown that resistances agree with the recent
experiments of anisotropic compressible states and the states have negative
pressure. As implications, the collapse phenomena of the integer quantum Hall
effect are discussed.Comment: 4 pages, 5 figures, to be published in Physica
Current distribution in Hall bars and breakdown of the quantum Hall effect
A numerical study is made of current distribution in small Hall bars with
disorder. It is observed, in particular, that in the Hall-plateau regime the
Hall current tends to concentrate near the sample edges while it diminishes on
average in the sample interior as a consequence of localization. Also reported
is another numerical experiment on a related, but rather independent topic, the
breakdown of the quantum Hall effect. It is pointed out that the competition of
the Hall field with disorder in the sample interior, an intra-subband process,
can account for both the magnitude and magnetic-field dependence (proportional
to B^{3/2}) of the critical breakdown fields observed experimentally.Comment: 6 pages, Revtex, 3 figures, ep2ds-1
Observation of the Ettingshausen effect in quantum Hall systems
Evidence of the Ettingshausen effect in the breakdown regime of the integer
quantum Hall effect has been observed in a GaAs/AlGaAs two-dimensional electron
system. Resistance of micro Hall bars attached to both edges of a current
channel shows remarkable asymmetric behaviors which indicate an electron
temperature difference between the edges. The sign of the difference depends on
the direction of the electric current and the polarity of the magnetic field.
The results are consistent with the recent theory of Akera.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Theory of Current-Induced Breakdown of the Quantum Hall Effect
By studying the quantum Hall effect of stationary states with high values of
injected current using a von Neumann lattice representation, we found that
broadening of extended state bands due to a Hall electric field occurs and
causes the breakdown of the quantum Hall effect. The Hall conductance agrees
with a topological invariant that is quantized exactly below a critical field
and is not quantized above a critical field. The critical field is proportional
to and is enhanced substantially if the extended states occupy a
small fraction of the system.Comment: 5 pages, RevTeX, final version to appear in PR
Field-induced breakdown of the quantum Hall effect
A numerical analysis is made of the breakdown of the quantum Hall effect
caused by the Hall electric field in competition with disorder. It turns out
that in the regime of dense impurities, in particular, the number of localized
states decreases exponentially with the Hall field, with its dependence on the
magnetic and electric field summarized in a simple scaling law. The physical
picture underlying the scaling law is clarified. This intra-subband process,
the competition of the Hall field with disorder, leads to critical breakdown
fields of magnitude of a few hundred V/cm, consistent with observations, and
accounts for their magnetic-field dependence \propto B^{3/2} observed
experimentally. Some testable consequences of the scaling law are discussed.Comment: 7 pages, Revtex, 3 figures, to appear in Phys. Rev.
Electronic Processes at the Breakdown of the Quantum Hall Effect
Microscopic processes giving the energy gain and loss of a two-dimensional
electron system in long-range potential fluctuations are studied theoretically
at the breakdown of the quantum Hall effect in the case of even-integer filling
factors. The Coulomb scattering within a broadened Landau level is proposed to
give the gain, while the phonon scattering to give the loss. The energy balance
equation shows that the electron temperature T_e and the diagonal conductivity
sigma_{xx} exhibit a bistability above the lower critical electric field
E_{c1}. Calculated values of E_{c1} as well as T_e and sigma_{xx} at E_{c1} are
in agreement with the observed values in their orders of magnitude.Comment: 4 pages, 2 Postscript figures, submitted to the Journal of the
Physical Society of Japa
Magnetic von-Neumann lattice for two-dimensional electrons in the magnetic field
One-particle eigenstates and eigenvalues of two-dimensional electrons in the
strong magnetic field with short range impurity and impurities, cosine
potential, boundary potential, and periodic array of short range potentials are
obtained by magnetic von-Neumann lattice in which Landau level wave functions
have minimum spatial extensions. We find that there is a dual correspondence
between cosine potential and lattice kinetic term and that the representation
based on the von-Neumann lattice is quite useful for solving the system's
dynamics.Comment: 21pages, figures not included, EPHOU-94-00
Hydrodynamic Equation for the Breakdown of the Quantum Hall Effect in a Uniform Current
The hydrodynamic equation for the spatial and temporal evolution of the
electron temperature T_e in the breakdown of the quantum Hall effect at
even-integer filling factors in a uniform current density j is derived from the
Boltzmann-type equation, which takes into account electron-electron and
electron-phonon scatterings. The derived equation has a drift term, which is
proportional to j and to the first spatial derivative of T_e. Applied to the
spatial evolution of T_e in a sample with an abrupt change of the width along
the current direction, the equation gives a distinct dependence on the current
direction as well as a critical relaxation, in agreement with the recent
experiments.Comment: 4 pages, 1 Postscript figure, corrected equations, to be published in
J. Phys. Soc. Jpn. 70 (2001) No.
Metal-Insulator Transition and Spin Degree of Freedom in Silicon 2D Electron Systems
Magnetotransport in 2DES's formed in Si-MOSFET's and Si/SiGe quantum wells at
low temperatures is reported. Metallic temperature dependence of resistivity is
observed for the n-Si/SiGe sample even in a parallel magnetic field of 9T,
where the spins of electrons are expected to be polarized completely.
Correlation between the spin polarization and minima in the diagonal
resistivity observed by rotating the samples for various total strength of the
magnetic field is also investigated.Comment: 3 pages, RevTeX, 4 eps-figures, conference paper (EP2DS-13
Integer Quantum Hall Effect with Realistic Boundary Condition : Exact Quantization and Breakdown
A theory of integer quantum Hall effect(QHE) in realistic systems based on
von Neumann lattice is presented. We show that the momentum representation is
quite useful and that the quantum Hall regime(QHR), which is defined by the
propagator in the momentum representation, is realized. In QHR, the Hall
conductance is given by a topological invariant of the momentum space and is
quantized exactly. The edge states do not modify the value and topological
property of in QHR. We next compute distribution of current based
on effective action and find a finite amount of current in the bulk and the
edge, generally. Due to the Hall electric field in the bulk, breakdown of the
QHE occurs. The critical electric field of the breakdown is proportional to
and the proportional constant has no dependence on Landau levels in
our theory, in agreement with the recent experiments.Comment: 48 pages, figures not included, some additions and revision
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